Lead Bismuth Pb-Bi FLOTATION
Many times we can hear that copper concentrates have contaminants which affect the incomes to be obtained by commercialization. Well, one of the worst contaminant is bismuth because is difficult to remove during smelting process and the metallic copper to be obtained at the end of the process will be brittle and consequently its mechanical properties will be very bad. Ergo, the objective is focused to minimize the bismuth content in the copper concentrate which is usually chalcopyrite.
The bulk copper concentrate has no only chalcopyrite, also lead as galena and bismuth minerals such as cosalite, bismuthinite, aikinite, and wittichenite. The idea is separate lead and bismuth minerals from chalcopyrite by flotation. Thus, the copper concentrate will not have penalties for bismuth. Ideally, the bismuth content must be less than 1000 ppm.
Considering the fact that lead and bismuth are very close in the periodic table (number atomic: 82 Pb, 83 Bi), they can have similar behaviour during flotation. It means that collection and depression is very similar for both. So, applying the lead-copper separation technique is possible separate bismuth and copper too.
There are several methods for lead-copper separation. But, perhaps, the more common is employing NaCN as depressant for chalcopyrite, and also use a collector for improving bismuth flotation. The collector can be sodium isopropyl xanthate (SIPX). Previously to add sodium cyanide can be added activated carbon which absorbs reagents from mineral surfaces and residual reagents from the slurry.
The flotation gas to be used in roughing and cleaning flotation can be air or nitrogen, but preferently the latter because sodium cyanide is susceptible to be oxidized. If oxygen is present, the formation of cyanates and thiocyanates is favored; also the collector could have any grade of overoxidation. Air can be used, but the NaCN consumption will be higher, maybe twice than the amount added with nitrogen. The NaCN dosage during roughing flotation is about 70 to 80% of the total dosage. Thus, is good choice employ nitrogen as flotation gas.
Use a frother like MIBC is optional because its addition will depend of froth characteristics (i.e. texture, viscosity, bubble size)
Cleaning stages can be done employing mechanical or column cells. The latter one is very useful because washed water can eliminate fine particles of gangue present on the bubbles. During the cleaning stage is very important the NaCN dosage since some chalcopyrite particles can still present in the froth.
A key aspect in the separation is the redox potential. This value has direct relation with the NaCN dosage.
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